Flame ionization detector



July 15, 1969 JENTZSCH ET AL FLAME IONIZATION DETECTOR Filed June 9. 1966 v04 me E 500/? C E III R SUPPL v ELECTR/CHL 2 Sheets-Sheet 1 7'0 RECORDER SOURCE OF CflRR/ER 6W5 END SflMPLE [IND COMBUSTIBLE 6/95 I N VENTORS 11 T TORNE Y.

FLAME IONI ZATION DETECTOR 2 Sheets-Sheet 2 Filed June 9. 1966 172 TOR NF Y.

United States Patent "ice 3,455,657 FLAME IONIZATION DETECTOR Dietrich Jentzsch, and Klaus Kuhne, Uberlingen (Bodensee), Germany, assignors to Bodenseewerk Perkin- Elmer & Co., G.m.b.H., Uberlingen (Bodensee), Germany, a corporation of Germany Filed June 9, 1966, Ser. No. 556,299, Claims priority, application Germany, Oct. 14, 1965, B 84,108 Int. Cl. GOln 33/00 US. Cl. 23-254 Claims ABSTRACT OF THE DISCLOSURE A flame ionization detector includes a burner nozzle supported and insulated from a detector base and an electrically conductive air pipe including an air converging nozzle positioned within the pipe. Means insulate the air pipe from the base and position the pipe with respect to the burner nozzle so that the burner nozzle extends into the air converging nozzle. An electrically conductive coupling is provided between the burner nozzle and air pipe. An arrangement of this type substantially maintains the linearity of a detector as its size is reduced.

The present invention relates to detectors for use with chromatographic apparatus. The invention relates more particularly to flame ionization detectors.

Flame ionization detectors employed in chromatographic apparatus are adapted for detecting the concentration of components of a sample being analyzed. These components, which are successively eluted from a separating column of the apparatus, are introduced into a burner flame and accompanying variations in ionization resulting from combustion of the components are sensed.

Flame ionization detectors include a chamber having a burner nozzle operating also as an electrode and a second electrode spaced with respect to the burner nozzle. An electric potential is applied between these electrodes through an electrical impedance. A series circuit is thereby formed and includes the source of potential, the electrical impedance and the flame resistance.

The sample components are introduced into the chamber via a carrier gas along with a combustible gas, and air for sustaining combustion. Burning of the component causes the flame resistance to vary and a current flowing in the series circuit varies accordingly. Corresponding changes in voltage developed across the external impedance can thereby be amplified in a manner for operating recording instruments.

The resistance of the flame is high and is on the order of 10 ohms. Combustion of a sample component greatly increases the flame conductivity. However, the corresponding resistance of the flame still remains relatively high and the electric potential is therefore applied between the electrodes through a relatively high impedance in order to cause detectable variations in voltage when a component is burned. This impedance is generally on the order of 10 to 10 ohms. As a result, leakage resistances in the circuit must be given serious consideration. For this and other reasons, it is known to support and space the burner nozzle from a detector base by means exhibiting relatively high electrical insulation characteristics at the high temperature encountered in the burner. Suitable support materials are the refractory materials, including ceramic.

A particularly advantageous form of flame ionization detector includes the described burner nozzle supported and electrically insulated from a detector base plate. In

3,455,657 Patented July 15, 1969 addition, an elongated air pipe having an internal air converging nozzle is provided. This pipe is positioned about the burner nozzle and spaced relative thereto so that the mouth of the burner nozzle is positioned in and extends slightly through the air converging nozzle. The flow of air is thereby concentrated at the flame and improved combustion and reduced air consumption are accomplished. In addition, the air pipe chamber shields the flame from the remaining air space of the detector and thereby increases sensitivity by reducing interfering influences.

It is desirable to reduce the physical size of this form of detector. However, such a reduction is accompanied by a decrease in the range of linearity of the detector and small sample quantities could no longer be or barely are detected.

Accordingly, it is an object of the present invention to provide an improved flame ionization detector.

Another object of the invention is to provide a detector of the type referred-to of reduced dimensions and in which linearity is maintained over a relatively large range.

In accordance with the present invention, a flame ionization detector includes a burner nozzle supported and insulated from a detector base and an electrically conductive air pipe including an air converging nozzle positioned within the pipe. Means insulate the air pipe from the base and position the pipe with respect to the burner nozzle so that the burner nozzle extends into the air converging nozzle. An electrically conductive coupling is provided between the burner nozzle and air pipe. An arrangement of this type substantially maintains the linearity of the detector of reduced dimensions.

In accordance with another feature of the invention, the electrically conductive coupling means is adapted for facilitating maintenance of the burner assembly and providing firm contact between the pipe and burner nozzle under the relatively severe environmental conditions existing within the detector.

These and other objects of the invention will become apparent with reference to the following specifications and drawings wherein:

FIGURE 1 is a cross-sectional view of a flame ionization detector constructed in accordance with features of the invention;

FIGURE 2 is an enlarged cross-sectional view of the air piping and burner nozzle members of the detector of FIGURE 1; and

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2.

Referring now to FIGURE 1, a detector block indicated generally as 7 is shown supporting a burner assembly. The burner assembly includes a generally tubular support member 8 screwed into the block, a tubular electrical insulating member 9 inserted in the member 8 and a burner nozzle 10 having an exhaust orifice positioned on insulating member 9. A sample to'be burned is derived from a source 27. The sample is conveyed by a carrier gas along with a combustible gas from the source 27 through suitable tubing 23 to the block 7 and to the burner assembly. Air which is provided to support combustion is derived from a source 26 and conducted through tubing 17 to the block 7. The air passes through passages in the block 7 and enters the lower combustion chamber 18 near the nozzle support member 8.

An elongated electrically conductive, generally cup shaped air pipe 11 is supported in a suitably orientated position on the detector block 7 by a block 6 formed of insulative material. This piping member as indicated hereinbefore, is advantageous in that it concentrates the incoming air at the flame to provide improved combustion and air consumption while shielding the flame from interfering influences within the chamber. The air piping member includes an internal air converging nozzle 13. In FIGURES l and 2, the nozzle 13 is shown formed as an integral segment 12 of the pipe. The pipe 11 and burner nozzle are relatively positioned so that the burner nozzle 10 extends into and protrudes slightly above the nozzle. Air enters the lower chamber 18 which is enclosed by the block 7, the insulating ring 6, and a lower surface of the segment 12. The nozzle converges upwardly, and air current is thereby directed and concentrated at the flame. An upper portion of the air pipe shields the flame from undesirable surrounding influences within the chamber.

An electrical potential is derived from a source 25 and coupled to the piping member 11 by a lead 14. The burner nozzle 10 is maintained in electrical contact with the air piping 11 and thus at the same potential by contact means 15, the arrangement of which is indicated in greater detail hereinafter. By this arrangement, the burner nozzle and pipe are maintained at a same fixed potential and are electrically insulated from the ground or mass potential of the block. The burner nozzle therefore comprises one electrode of the detector. A potential is also applied from the source 25 to a second electrode 24 via a resistance 30 and a lead extending through an insulator 19 which is arranged near the outer end of a tubular extension 20. The tubular extension removes the insulator 19 from the vicinity of the flame in order to reduce resistance variations accompanying increased temperature. The flame is ignited by a conventional ignition coil indicated generally as 22.

A cover 21 is positioned on the block 7 and encloses the burner and electrode assemblies. Means not shown for venting the chamber are provided to exhaust burned gases.

In operation, a relatively small current will flow in the series circuit formed by the potential source 25, burner nozzle electrode 10, the flame, electrode 24 and resistance 30 when the carrier gas, combustible gas and air are burned. The combustible gas can be hydrogen while a carrier gas can be some inert gas such as oxygen or nitrogen. A sample component conveyed to the burner nozzle reduces the flame resistance because of ionization and a corresponding variation in current flow occurs. This variation causes a change in the voltage drop across the resistance 30. An amplifier 31, which can be a DC amplifier, amplifies this variation to a level suitable for operating recording instruments.

FIGURES 2 and 3 illustrate in greater detail a means for providing conductive coupling between the air pipe 11 and the burner nozzle 10. A spring is formed, as shown in FIGURE 3, and positioned in a recess in an inner wall 16 of the air pipe 11. The spring has a generally circular configuration for a large segment of its length and is bent inwardly near its ends to abut the burner nozzle 10. In addition to providing the desired electrical contact, an arrangement of this form advantageously facilitates the removal of the burner assembly for maintenance. Further, the spring 15 is shown to comprise a bimetallic arrangement of two metallic strips of metal. The bimetallic spring is adapted to increase its contact pressure between the pipe and burner nozzle as the burner temperature increases. A reliable contact is therefore assured at the relatively high burner temperature existing in the chamber.

A flame ionization detector has been described which is adapted for maintaining linearity at reduced physical dimensions. In addition, an arrangement is described for providing conductive coupling between the air pipe and burner nozzle at high temperatures and is adapted for facilitating maintenance of the burner nozzle.

While I have illustrated and described a particular embodiment of my invention, it will be understood that various modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

I claim:

1. A flame ionization detector of the type wherein a sample, a combustible gas and air are introduced thereto for burning the sample comprising:

a detector support means,

an elongated electrically conductive air pipe having a convergent nozzle positioned within the pipe, first means supporting the air pipe on said detector support means, a burner nozzle, second means supporting said burner nozzle on said detector support means and positioning said burner nozzle in said convergent nozzle in a manner for providing that an exhaust orifice of said burner nozgle protrudes from said convergent nozzle, and

means providing an electrical conductive coupling between said air pipe and said burner nozzle.

2. A flame ionization detector of the type wherein a sample, a combustible gas, and air are introduced thereto for burning the sample, comprising:

a detector support means,

an elongated electrically conductive air pipe having a convergent nozzle positioned within the pipe,

first means supporting the pipe on said detector support and electrically insulating the pipe from said detector support means,

a burner nozzle,

second support means supporting and electrically insulating said burner nozzle on said detector support means and positioning said burner nozzle in said convergent nozzle, and

means providing an electrical conductive coupling between said air pipe and said burner nozzle.

3. The detector of claim 2 wherein said burner nozzle includes an exhaust orifice and said second support means positions said burner nozzle in a manner for providing that the exhaust orifice of the burner nozzle protrudes from said convergent nozzle.

4. A flame ionization detector of the type wherein a sample, a combustible gas, and air are introduced thereto for burning the sample comprising:

a detector support block,

an elongated electrically conductive air piping member including a convergent nozzle positioned within said member,

a burner nozzle,

electrical insulating means for supporting said pipe and saidburner nozzle on said detector support block and positioning said burner nozzle in said convergent nozzle, and

means providing an electrical conductive coupling between said pipe and said burner nozzle.

5. The detector of claim 4 wherein said pipe is cylindricaily shaped.

6. The detector of claim 4 wherein said conductive coupling means comprises a resilient contact.

7. The detector of claim 6 wherein said contact comprises bi-metallic metals adapted to expand under elevated temperatures.

8. The detector of claim 6 wherein said burner nozzle includes an exhaust orifice and the insulating support means relatively position said burner nozzle and pipe for providing that the exhaust orifice protrudes from said convergent nozzle.

9. A flame ionization detector of the type wherein a sample, a combustible gas, and air are introduced thereto for burning the sample comprising:

an electrically conductive detector block,

a generally cup shaped air pipe having a bottom thereof formed as a convergent nozzle,

an electrical insulator supporting said pipe on said detector block,

an electrically conductive burner nozzle having an exhaust orifice,

anelectrical insulator supporting said burner nozzle on said detector block and positioning said burner nozzle in said convergent nozzle and in a manner for providing that said exhaust orifice protrudes slightly from said convergent nozzle,

said air pipe having a recessed surface formed on an inner surface thereof, and

a resilient contact positioned against said recessed surface and adapted for contacting said burner nozzle.

10. A fiame ionization detector apparatus comprising:

a detector support block,

an elongated electrically conductive air piping member including a convergent nozzle positioned within said member,

a burner nozzle,

electrical insulating means supporting said pipe and 15 an electrode positioned in closely spaced relation to said burner nozzle,

means for applying an electric potential between said pipe and said electrode,

means for supplying a combustion supporting gas to said air pipe, and

means for supplying a combustible gas and a sample component being analyzed to said burner nozzle.

References Cited UNITED STATES PATENTS 3,086,848 4/1963 Reinecke. 3,330,960 7/1967 Rich. 3,372,000 3/ 1968 Gallaway et al.

MORRIS O. WOLK, Primary Examiner R. M. REESE, Assistant Examiner US. Cl. X.R. 

